1. Field of the Invention
The present invention relates to a machine for removing contaminants from a fiber suspension, and, more particularly, to a flotation machine used for removing contaminants from a fiber suspension.
2. Description of the Related Art
A paper-making machine receives a prepared fiber suspension and produces a fiber web, such as a paper web. The fiber suspension is prepared from a source of fiber, such as wood fiber, within a stock preparation system. The stock preparation system may include a flotation machine which is used to float contaminants to the top of the suspension for removal thereof. Typically, the fiber suspension is at a relatively high temperature as a result of the various mechanical forces which are applied thereto and chemical reactions which occur therein. Contaminants within the fiber suspension in the form of particulates, such as varnish particles, dirt, etc. are relatively unaffected by the higher temperature of the fiber suspension and may be adequately floated to the top of the fiber suspension for removal. However, contaminants within the fiber suspension may also be in the form of various waxes which are contained within recycled paper. The waxes are transformed into colloidal particles within the fiber suspension at the higher temperatures at which the fiber suspension is typically transported into the flotation machine. Accordingly, the flotation process within the flotation machine is ineffective to adequately remove the colloidal wax from the fiber suspension.
What is needed in the art is a flotation machine and corresponding method of operation which allow effective removal of wax contaminants within the fiber suspension.
The present invention provides a flotation machine which injects low temperature gas into the fiber suspension to cause clumping of the colloidal wax and thereby allow the wax to be floated to the top and removed.
The invention comprises, in one form thereof, a flotation machine for removing a contaminant from a fiber suspension, including a flotation cell having an inner chamber. At least one gas injector injects a gas into the fiber suspension within the inner chamber at a temperature below 20xc2x0 C. to cause the wax to clump within the fiber suspension. A wax removal device includes an elongate element positioned at and configured to move along a top of the inner chamber to remove contaminants from the fiber suspension.
The invention comprises, in another form thereof, a method of removing wax from a fiber suspension. A flotation machine is provided which includes at least one flotation cell having an inner chamber. The fiber suspension is transported into the inner chamber. A gas is injected into the fiber suspension within the inner chamber at a temperature below 20xc2x0 C. to cause the wax to clump within the fiber suspension. The clumped wax is removed from the fiber suspension.
An advantage of the present invention is that the wax within the fiber suspension is caused to clump, thereby allowing flotation and removal thereof.
Another advantage is that the clumped wax may be removed with different types of removal devices.